JPH0281337A - fiber optic head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber head suitable for detecting defocus in optical information processing devices such as optical disks, optical cards, and optical tapes.

[Conventional technology]

In an optical disc device, when accessing an arbitrary track on the disc surface, the optical head is moved in the radial direction of the disc. In order to perform this access at high speed, a small and lightweight optical head is required. but,
The housing of a conventional optical head includes a semiconductor laser as a light source, a lens system to focus the laser light into a minute spot on the disk surface, and a beam splitter to separate the disk reflected light from the semiconductor laser emitted light. It also incorporates a special optical system and photodetector to detect defocus and track misalignment from the separated disc reflected light, making it difficult to make it smaller and lighter. Additionally, if the position of the semiconductor laser shifts due to deformation of the housing due to temperature changes, etc., the position of the disk reflected light on the photodetector surface also shifts, which tends to cause offsets in the defocus detection signal and track misalignment detection signal. There was a problem.

Therefore, in Japanese Patent Application Laid-Open No. 55-15039, two semiconductor lasers that emit beams for detecting defocus are arranged symmetrically with respect to a semiconductor laser for reproduction, etc. in the optical axis direction, and
An automatic focus adjustment device has been proposed in which a defocus detection signal is obtained from the difference between the output signals of two photodetectors placed behind a semiconductor laser for defocus detection (in the opposite direction to the disk). In this device, the light emitting position of the semiconductor laser and the disk reflection surface are almost in a point imaging relationship due to the lens system, so the two semiconductor lasers for defocus detection are individually shifted in the lateral direction with respect to the optical axis. Even if.

Offset is less likely to occur in the defocus detection signal.

[Problem to be solved by the invention]

Since the focusing accuracy of optical discs and the like is usually about ±1 μm, focusing adjustment is required when assembling the optical head. In order to perform focusing adjustment in the above conventional technology, there are two methods: (1) adjusting the position in the optical axis direction by equalizing the emitted light amount of two lasers for focus detection, (2) adjusting the position of the two lasers for focus detection in the optical axis direction; There is a method to shift the disc, but in method (■), if the disc shifts from the focal position,
The defocus detection signal becomes asymmetrical depending on the direction in which the disk is displaced, and the automatic focus control tends to oscillate, which is undesirable, so method (2) is preferable.

By the way, the image field of a collimating lens such as an optical head is usually about 500 μm, so three separately packaged semiconductor lasers are spaced 250 μm in the direction perpendicular to the optical axis.
Therefore, three semiconductor laser chips must be arranged in a hybrid manner on one mount.

However, it is not possible to adjust the chip position while making the laser chip emit light while it is incorporated in an optical head.

Therefore, with the above-mentioned conventional technology, focusing adjustment is difficult. There was a problem.

An object of the present invention is to provide an optical fiber head that is small and lightweight, has stable performance against misalignment of optical components, and is easy to adjust focusing.

[Means to solve the problem]

The above purpose is to provide a first optical fiber that emits a first laser beam for defocus detection, and a first optical fiber that emits a first laser beam for defocus detection, as a light source in an optical head, in proximity to an optical fiber that emits a laser beam for recording or reproducing information. a second beam that emits two laser beams;
The optical fibers are arranged so that their laser beam emitting end positions are equally spaced back and forth from the recording/reproducing optical fiber emitting end position. Furthermore, a first photodetector receives the amount of light reflected from the disc that is incident on the first optical fiber, and a second photodetector that receives the amount of light that is also incident on the second optical fiber.
A photodetector is provided on the fixed optical system side, and a defocus detection signal is obtained from the difference between the outputs of the first and second photodetectors.

[Effect]

The defocus detection principle of the present invention will be explained using FIG. Radiation end 61a of optical fiber 60a for recording or reproduction
A laser beam 62a emitted from the laser beam 62a is focused on the disk 64 by a focus lens system 63 as a focal point 65a. On the other hand, the laser beam 62b emitted from the radiation end 61b of the first optical fiber 60b for defocus detection is at the focal point 6.
5b, the laser beam 62c emitted from the radiation end 61c of the second optical fiber 60c is focused at a focal point 65c.
focus towards. After being reflected by the disk 64, the laser beams 62b and 62c become beams that diverge from points 66b and 66c. Then, the laser beam 62b is focused on a focal point 66b by the lens system 63, and the laser beam 62b is focused on a focal point 66b.
2c is focused at a focusing point 66c. Radiation ends 61b and 61c
is shifted by the same distance in the opposite direction from the radiation end 61a, so the diameter of the laser beam 62b after reflection at the radiation end 61b is equal to the diameter of the laser beam 62c after reflection at the radiation end 61c, and the diameter of the laser beam 62c after reflection at the radiation end 61c is equal. The same amount of light is incident on 60b and 60c. When the disk 64 shifts to the position of the focal point 65b of the first laser beam 62b,
Since the focusing point 66b is located at the radiation end 61b, the amount of light incident on the first optical fiber 60b becomes maximum, and on the other hand,
Since the focal point 66c is further shifted in the direction of the lens system 63, the amount of light incident on the second optical fiber 60c is reduced. Conversely, the disk 64 is the focal point 65 of the second laser beam 62c.
When shifted to position c, the focusing point 66c comes to the position of the radiation end 61c, so the amount of light incident on the second optical fiber 60c becomes maximum.On the other hand, the focusing point 66b shifts in the opposite direction to the lens system 63, so the amount of light incident on the second optical fiber 60c becomes maximum. The amount of light incident on the first optical fiber 60b decreases.

FIG. 5 shows the relationship between the position of the disk 64 and the amount of light incident on the first and second optical fibers 60b and 60c. The horizontal axis 70 is the position of the disk 64, and the vertical axis @71 is the amount of light incident on the optical fibers. be. Disk 64 is focal point 6
The case at position 5b is indicated by point 73', and the amount of light incident on the first optical fiber becomes maximum at point 73' as shown by curve 72b. On the other hand, the case where the disk 64 is at the focal point 65c is indicated by a point 731, and the amount of light incident on the second optical fiber is maximum at the point 731 as shown by a curve 72c.

Further, the case where the disk 64 is at the focal point 65a is indicated by a point 73, and in this case, the curves 72b and 72c match. The vertical axis 71 shown in FIG. 5 also corresponds to the output of the first and second photodetectors connected to the optical fibers 60b and 60c on the fixed optical system side. In FIG. 6, the horizontal axis 70 indicates the same position of the disk 64 as in FIG. 5, and the vertical axis 75 indicates the difference signal between the first and second photodetector outputs, as shown by a curve 76. A defocus detection signal can be obtained.

In FIG. 4, the optical fiber radiation end 61a or 61b
Alternatively, the lens system 63 allows the lens 61c and the disk 64 to have a nearly point imaging relationship. Therefore, three optical fibers 6
Even if 0a, 60b, and 60c are independently shifted in the vertical direction of the paper, the three laser beams return to the radiation end of the optical fiber from which they were emitted, so the optical fiber 6
The amount of light incident on 0b and 60c does not change, so no error occurs in the defocus detection signal.

Further, focusing adjustment can be performed by adjusting the position of the optical fiber in the optical axis direction while emitting laser light from the optical fiber.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
FIG. 1 is a diagram showing the configuration of an optical fiber head using the defocus detection optical system of the present invention.

Recording/reproducing laser beam 2 emitted from the semiconductor laser 1a
The beam a passes through the beam splitter 3, enters the optical fiber 5a with an outer diameter of 30 μm through the condensing lens 4, passes through the core portion of the optical fiber 5a with a diameter of 10 μm, and is emitted from the radiation end 17a at a divergence angle of about ±15°. The light is emitted, becomes a parallel light beam by a collimating lens 6 with NA=0.25, is reflected by a mirror prism 7, and is imaged as a spot 9a on the surface of the optical disk 10 by a focus lens 8 with NA=0.5.

Recording/reproducing laser beam 2a focused as a spot 9a
is reflected by the disk 10, travels backward along the above-mentioned outward path, reaches the beam splitter 3, is reflected by the beam splitter, is received by the photodetector 11a, and outputs a signal 12a. On the other hand, the first defocus detection laser beam 2b emitted from the semiconductor laser 1b passes through the optical fiber 5b with an outer diameter of 30 μm, is emitted from the core portion of the radiation end 17b with a diameter of 10 μm, and is focused on the focal point 9b. Further, the second defocus detection laser beam 2c emitted from the semiconductor laser 1c passes through an optical fiber 5c with an outer diameter of 30 μm, and is emitted from the core portion of the radiation end 17c with a diameter of 10 μm, and is focused at a focal point 9c.
focus on. The radiation end 17b of the optical fiber 5b is shifted from the radiation end 17a of the optical fiber 5a toward the collimating lens 6 side, and the radiation end 17c of the optical fiber 50 is shifted in the opposite direction from the radiation end 17a by an equal distance, for example, 6 μm. The focal points 9b and 90 are spaced at equal distances from the spot 9a in opposite directions, for example 1.5μ.
It is shifted by m. Also, the distance between the three optical fibers is 50 μm, and the spot 9a.

9b and 9c are spaced apart by 25 μm. The laser beams 2b and 20 reflected by the disk 10 are connected to the optical fiber 5, respectively.
b and 50, and a part of them is focused toward the radiation end 17b.
and 17c, passes through optical fibers 5b and 50,
This time, the light is reflected by the beam splitter 3 and received by the photodetectors flb and lie, which output signals 12b and 12c. Signals 12b and 12c are input to a differential circuit 13 and become a defocus detection signal 14. The defocus detection signal 14 is input to a focusing actuator 15 that moves the focus lens 8 in the lens optical axis direction.

According to the defocus detection principle of the present invention described above.

The disk 10 is the spot 9 of the recording/reproducing laser beam 2a.
In the focused state at position a, the amounts of light incident on the optical fibers 51) and 50 and received by the photodetectors 11b and llc are equal, and the defocus detection signal 14 is at zero level. The disk 10 is the first laser beam 2 for detecting defocus.
When the focal point of b shifts in the direction of 9b, as shown in FIG.
The amount of light incident on the first optical fiber 5b increases, and the amount of light incident on the first optical fiber 5b increases.
Since the amount of light incident on the optical fiber 50 decreases, the defocus detection signal 14 becomes a positive level. - On the other hand, when the disk 10 shifts in the direction of the focal point 9C of the laser beam 2C,
The amount of light incident on the first optical fiber 5b decreases, and the amount of light incident on the first optical fiber 5b decreases.
Since the amount of light incident on the optical fiber 50 increases, the defocus detection signal 14 becomes a negative level. Therefore,
Since the direction and amount of displacement of the disk 10 is known, automatic focus control is achieved by the focusing actuator 15.

For tracking control, for example, a tracking actuator 16 that moves the output signal 12a of the photodetector 11a and the focus lens 8 in the direction of track deviation can be used. FIG. 2(a) shows a certain track 20 on the surface of the disk 10, and along the track 20, uneven pits 21a and 22b are provided slightly shifted on both sides. When the recording/reproducing spot 9a scans the track 20, the output signal 12a of the photodetector 11a is as shown in FIG.
), as shown in the signal waveform 24, the uneven pits 21a and 2
It decreases to the same extent at 1b. When the spot 9a shifts downward from the track 20 and scans on the dotted line 22, the output signal 12a decreases greatly at the uneven pit 21a, as shown in the signal waveform 25 in FIG. 2(c). It is small at the uneven pit llb, and conversely, when scanning on the dotted line 23, as shown in the signal waveform 26 of FIG. 2(d).

The decrease in the uneven pit 21a is small, and the decrease in the pit 21b is large. Therefore, the output signal 12a of the photodetector 11a is
By comparing the signal levels modulated by the uneven pits 21a and 21b, a track deviation detection signal can be obtained, so that tracking control can be achieved using the tracking actuator 16.

The information recorded on the track is reproduced by the photodetector 11a.
It is well known that information can be recorded from the output signal 12a of the semiconductor laser 1a by pulse intensity modulating the output of the semiconductor laser 1a.

With the double wavy line 18 as the boundary, the parts on the semiconductor laser and photodetector side are fixed inside the optical disk device, and the parts on the focus lens side are built into the movable optical head. According to the example, the parts of the moving optical head are smaller than those of the prior art, making it possible to achieve a reduction in size and weight.

Furthermore, as mentioned above, within the moving optical head section,
Even if various parts shift, the point imaging relationship is maintained, so no errors occur in the defocus detection signal.

Focusing adjustment can be performed by shifting the optical fiber 5b or 5c in the optical axis direction, and it is possible to generate a defocus detection signal that is symmetrical with respect to the disc displacement direction.

FIG. 3 shows another embodiment of the present invention, and parts with the same numbers as in FIG. 1 perform the same functions as in FIG. 1, so a description thereof will be omitted. The laser beam emitted from the semiconductor laser 41 is separated by the diffraction grating 42 into 0th-order diffracted light 43a and plus and minus 1st-order diffracted lights 43b and 43c. The ratio of their light intensities is, for example, 7 for the O-order diffracted light and 1 for the ±1st-order diffracted light. The 0th order diffracted light 43a is transmitted through the optical fiber 45
a and is used as a laser beam for recording and reproduction.

The + and -1st order diffracted lights 43b and 43c are connected to the optical fiber 45.
b and 45c, and is used as a laser beam for detecting defocus according to the present invention. The disk 25 is assumed to move from the right side to the left side in the drawing, and in this embodiment, the focal points 47b and 47c of the laser beam for detecting defocus are arranged in advance of the recording/reproducing spot 47a. This is spot 47a
This is to prevent an imbalance between the two amounts of detected light due to the pits recorded. Thereby, during recording, it is possible to prevent variations in the light intensity of the laser beam for defocus detection due to recorded pits, and it is possible to obtain a more accurate defocus detection signal.

Further, the disk 55 includes, for tracking control,
For example, if there is a guide groove (group), a beam splitter 46 is used instead of the mirror prism 7 in FIG. The element output is connected to the differential circuit 51.
The track deviation detection signal 52 is obtained.

In this embodiment, in addition to the features described in the first embodiment, only one semiconductor laser is required, and a highly accurate defocus detection signal can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to realize an optical head in which the parts that move during access etc. are small and lightweight, and the performance is stable without causing errors in the detection signal even when the position of the optical components is shifted due to temperature changes etc. This makes it possible to realize an optical head that allows easy focusing adjustment during assembly.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical system showing one embodiment of the present invention, FIG. 2 is a diagram explaining the function of a part of the embodiment of FIG. 1, and FIG. 3 is a diagram showing another embodiment of the present invention. Optical system configuration diagram, Figure 4,
FIG. 5 and FIG. 6 are diagrams for explaining the present invention in detail. 1a, 1b, 1c... semiconductor laser, 5a, 5b,
5c...Optical fiber 8...Focus lens,
11a, 11b, llc... Photodetector, 41... Semiconductor laser, 42... Diffraction grating, 45a, 45b, 4
5c...Optical fiber 13...Differential circuit.

Claims (1)

[Claims] 1. A main optical fiber that emits a main laser beam for recording, reproducing, and erasing information from one end, and a defocus detection device for detecting a deviation between the focal position of the main laser beam and the information medium position. The laser beam emitting end position of the first sub optical fiber and the laser beam emitting end position of the second sub optical fiber are located at the same distance as that of the main optical fiber. An optical fiber head characterized in that the optical fiber head is arranged in front and back in the laser beam emission direction with respect to the main laser beam emission end position. 2. The optical fiber head according to claim 1, wherein the two focusing points of the first and second sub-laser beams on the information medium scan the information medium ahead of the spot of the main laser beam. Features an optical fiber head. 3. In the optical fiber head according to claim 1 or 2, the focus shift is determined by a difference signal between the outputs of the first and second photodetectors provided at the other ends of the first and second sub-optical fibers. An optical fiber head characterized by obtaining a detection signal.